MBR backup:
dd if=/dev/hda of=mbr_backup.bin bs=1 count=512
Swap if/of around to recover the entire MBR .
The partition table is located in MBR at 0x01BE (446) offset and consists of 4 records of 16 bytes.
To recover the partition table only:
dd if=mbr_backup.bin of=/dev/you-device bs=1 count=64 skip=446 seek=446